I can reinforce Ash's suggestion that a visit to DK's 'Emporium' is a good investment of your time. I visited last year (when I was on a house hunting mission oop north) and was amazed at the amount and diversity of stuff they have.
As far as their prices go......they sell and break so many bikes/ parts that they must have a good idea what the market will stand based on recent performance and exclusivity/ commonality/ availability and whilst buyers have E Bay and Couriers at their fingertips, prices will inevitably creep upwards through the auction process. That's Life I'm afraid.
If your Family (i.e, SWMBO) are dead set against a visit to DK....suggest that they go to Alton towers or Trentham gardens whilst you 'pop' over to DK's for 'an hour - or two'. Sorted.